Vehicle powertrains incorporate a multi-speed, automatic shifting power transmission to increase the effectiveness of the operating range of the internal combustion engine to provide for improved fuel economy and more efficient highway speed operation. The number of forward gear ratios available through the transmission has increased from two to five. The increased number of gear ratios requires an increased size and number of components at the transmission.
Many of the currently-available automatic shifting transmissions incorporate two or three planetary gear sets that are interconnected either directly or through friction devices to provide the desired gear ratios. The number of mechanical members increases with the number of gear ratios. Generally, an added gear ratio requires at least one additional friction device with the accompanying complexity in the control function. The added friction device (either a clutch or a brake) requires a plurality of friction plates, a piston, and return springs. These items require an increase in assembly time for the transmission. In the case of an added clutch, a housing must be provided, and a means for insuring against "centrifugal drift on" is necessary. In the case of a brake, additional machining in the transmission housing is required.